<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<!--
 Licensed to the Apache Software Foundation (ASF) under one or more
 contributor license agreements.  See the NOTICE file distributed with
 this work for additional information regarding copyright ownership.
 The ASF licenses this file to You under the Apache License, Version 2.0
 (the "License"); you may not use this file except in compliance with
 the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
-->
<html>
<head>
   <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
   <title>Apache Lucene Flexible Query Parser</title>
</head>
<body>

<h2>Apache Lucene Flexible Query Parser</h2>

<p>
This contrib project contains the new Lucene query parser implementation, which matches the syntax of the core QueryParser but offers a more modular architecture to enable customization.
</p>

<p>
It's currently divided in 2 main packages:
<ul>
<li>{@link org.apache.lucene.queryParser.core}: it contains the query parser API classes, which should be extended by query parser implementations. </li>
<li>{@link org.apache.lucene.queryParser.standard}: it contains the current Lucene query parser implementation using the new query parser API.</li>
</ul>
</p>

<h3>Features</h3>

    <ol>
        <li>Full support for boolean logic (not enabled)</li>
        <li>QueryNode Trees - support for several syntaxes, 
            that can be converted into similar syntax QueryNode trees.</li>
        <li>QueryNode Processors - Optimize, validate, rewrite the 
            QueryNode trees</li>
		<li>Processors Pipelines - Select your favorite Processor
		    and build a processor pipeline, to implement the features you need</li>
        <li>Config Interfaces - Allow the consumer of the Query Parser to implement
            a diff Config Handler Objects to suite their needs.</li>
        <li>Standard Builders - convert QueryNode's into several lucene 
            representations. Supported conversion is using a 2.4 compatible logic</li>
        <li>QueryNode tree's can be converted to a lucene 2.4 syntax string, using toQueryString</li>                          
    </ol>

<h3>Design</h3>
<p>
This new query parser was designed to have very generic
architecture, so that it can be easily used for different
products with varying query syntaxes. This code is much more 
flexible and extensible than the Lucene query parser in 2.4.X.
</p>
<p>
The new query parser  goal is to separate syntax and semantics of a query. E.g. 'a AND
b', '+a +b', 'AND(a,b)' could be different syntaxes for the same query.
It distinguishes the semantics of the different query components, e.g.
whether and how to tokenize/lemmatize/normalize the different terms or
which Query objects to create for the terms. It allows to
write a parser with a new syntax, while reusing the underlying
semantics, as quickly as possible.
</p>
<p>
The query parser has three layers and its core is what we call the
QueryNode tree. It is a tree that initially represents the syntax of the
original query, e.g. for 'a AND b':
</p>
<pre>
      AND
     /   \
    A     B
</pre>
<p>
The three layers are:
</p>
<dl>
<dt>QueryParser</dt>
<dd>
This layer is the text parsing layer which simply transforms the
query text string into a {@link org.apache.lucene.queryParser.core.nodes.QueryNode} tree. Every text parser
must implement the interface {@link org.apache.lucene.queryParser.core.parser.SyntaxParser}.
Lucene default implementations implements it using JavaCC.
</dd>

<dt>QueryNodeProcessor</dt>
<dd>The query node processors do most of the work. It is in fact a
configurable chain of processors. Each processors can walk the tree and
modify nodes or even the tree's structure. That makes it possible to
e.g. do query optimization before the query is executed or to tokenize
terms.
</dd>

<dt>QueryBuilder</dt>
<dd>
The third layer is a configurable map of builders, which map {@link org.apache.lucene.queryParser.core.nodes.QueryNode} types to its specific 
builder that will transform the QueryNode into Lucene Query object.
</dd>

</dl>

<p>
Furthermore, the query parser uses flexible configuration objects, which
are based on AttributeSource/Attribute. It also uses message classes that
allow to attach resource bundles. This makes it possible to translate
messages, which is an important feature of a query parser.
</p>
<p>
This design allows to develop different query syntaxes very quickly.
</p>

<h3>StandardQueryParser and QueryParserWrapper</h3>

<p>
The standard (default) Lucene query parser is located under
org.apache.lucene.queryParser.standard.
<p>
To make it simpler to use the new query parser 
the class {@link org.apache.lucene.queryParser.standard.StandardQueryParser} may be helpful,
specially for people that do not want to extend the Query Parser.
It uses the default Lucene query processors, text parser and builders, so
you don't need to worry about dealing with those.

{@link org.apache.lucene.queryParser.standard.StandardQueryParser} usage:

<pre>
      StandardQueryParser qpHelper = new StandardQueryParser();
      StandardQueryConfigHandler config =  qpHelper.getQueryConfigHandler();
      config.setAllowLeadingWildcard(true);
      config.setAnalyzer(new WhitespaceAnalyzer());
      Query query = qpHelper.parse("apache AND lucene", "defaultField");
</pre>
<p>
To make it easy for people who are using current Lucene's query parser to switch to
the new one, there is a {@link org.apache.lucene.queryParser.standard.QueryParserWrapper} under org.apache.lucene.queryParser.standard
that keeps the old query parser interface, but uses the new query parser infrastructure.
</p>

</body>
</html>
